Java Debug Issue

[T3rminus]

Here is the code:

Code: Select all

import java.util.Random;
class imp{
   public static void main (String [] args){
      Random rnum = new Random ();
      int red[]=new int[7];
      
      for(int roll=0; roll<1000; roll++){
         ++red[1+rnum.nextInt(6)];
      }
      
      System.out.println("Aray Num:\tTimes Shown:");
      
      for(int face=1;face<=red.length; face++){
         System.out.println(face+"\t"+red[face]);
         }
      }
   }


I am not getting any compilation errors. When I run it doies what it is supposed to, but there is an error at the end that says:

Code: Select all

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 7
   at imp.main(imp.java:14)

I cant see the error. The program does exactly what I want it to...

Thx in advance

-Phill

[JoeyPardella]

if you write to red[7] it'll be out of bounds because the 0 counts as first element.
so you'll have to nextInt(5) or red = new int[8]

[T3rminus]

Well if you watch this video the code is identical to his. Shouldn't this work. Or is my code wrong and I just dont know it???

http://www.youtube.com/watch?v=pHxtKDENDdE&NR=1&feature=fvwp

-Phill

[JoeyPardella]

ok I looked over the code again.

It's not the random stuff. but it IS worthy to know that random.nextInt(int i) gets values from 0 (including) to i (excluding). that's why new int[7] is fine.

what't NOT fine though is:

Code: Select all

for(int face=1;face<=red.length; face++){
          System.out.println(face+"\t"+red[face]);
       }

as a rule of thumb you can remember that it is never a good idea to write i<=something.length
it always has to be i<=something.length-1 or it can also be i<something.length.
but you can't read the array position on length. that'll throw an out of bounds exception.

here's the complete correct code:

Code: Select all

package test;

import java.util.Random;

public class Test {

   /**
    * @param args
    */
   public static void main(String[] args) {
      Random rnum = new Random ();
       int red[]=new int[7];
        
       for(int roll=0; roll<1000; roll++){
          ++red[1+rnum.nextInt(6)];
       }
        
       System.out.println("Aray Num:\tTimes Shown:");
        
       for(int face=1;face<red.length; face++){
          System.out.println(face+"\t"+red[face]);
       }

   }

}


edit: it's even right in the video dude.
also let me add that if you loop from i=1 to i<1000 It'll just loop 999 times and not 1000. that's a mistake he made in the video and I think you should move to some better sources than this.

[jpmut]

Now you should learn to read Java Error Messages. Saves a lot of debugging time.

It said:

Code: Select all

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 7
   at imp.main(imp.java:14)

Meaning, some array (say -temp-) item is being called by temp[7] and yet temp's size is less than or equal to 7, and this call happens in the function main() on the 14-th line of imp.java

The only call/reference of an array on that line is red[face], and the error tells us face=7 at some point which is not supposed to happen since we know red has size 7. How do we constrain the size of face then, fixing the condition in the for-loop.

[T3rminus]

Thx a lot for all of the help guys. I really need some encoragement to keep going with programming. I learn it really quickly but I cant stick with it for very long. Anyway thx. I will be going at it again really hard when I wake up. Keep up the good help.

-Phill

[MarkIntelhunter99]

Your program accessed more than the original array's length.

Code: Select all

import java.util.Random;
class Debug{
   public static void main (String [] args){
      Random rnum = new Random ();
      int red[]=new int[7];

      for(int roll=0; roll<1000; roll++){
         ++red[1+rnum.nextInt(6)];
      }

      System.out.println("Aray Num:\tTimes Shown:");

      for(int face=1;face<red.length; face++){
         System.out.println(face+"\t"+red[face]);
         }
      }
   }

and another way to Generate random number is

Code: Select all

class TestRandom{
   public static void main (String args[]) {
      int N = 1000, count = 0, number;
      double X;

      do{
         count++;
         X = Math.random();
         number = (int) Math.floor ( X * 1000 ) + 1;
         System.out.println(number);
      } while (count < N && 1 <= number && number <= 5);


   }
}

if you are trying to do so.

[fashizzlepop]

This is a quasi-necro. The problem looked solved and it's been more than half a year since the last post. No warning, just watch out.